To make a leg-type mobile robot, such as a bipedal mobile robot, perform an operation of, for example, moving a certain object by pushing, a desired gait for the robot is usually generated on the basis of a desired motion of the object according to a plan for moving the object (such as a plan that specifies the timing and the method for moving the object). Then, the motion of the robot is controlled such that the motion of the robot follows the generated desired gait (refer to, for example, Japanese Laid-Open Patent Application Publication No. H10-230485). When making the robot perform an operation of moving the object, the robot is subjected not only to a reaction force (external force) from a floor in the moving environment but also to a reaction force (external force) from the object, which is different from a case where the robot moves alone. For this reason, in order to secure stability of a posture of the robot, the desired gait is generated such that the so-called ZMP (Zero Moment Point) lies within a ground contact plane (within, more generally, the so-called supporting polygon) of the robot, taking also an influence attributable to the reaction force from the object into account.
Meanwhile, when linearly moving the object forward from the front of, for example, a bipedal mobile robot, a desired gait of the robot is usually generated such that the position-posture relationship between the robot and the object will be an appropriate position-posture relationship during the period of each step of the robot. In other words, the desired landing position/posture of the leg on a free leg side of the robot are determined such that a mean moving velocity of the object by the robot in the period of each step of the robot is equal to a mean moving velocity of the object in the period based on the plan for moving the object. In this case, the desired landing position/posture of the leg on the free leg side of the robot must be set within a range that satisfies a restrictive condition, such as a range within which the leg of the free leg side can be mechanically moved with respect to the leg of a supporting leg side. However, as long as the velocity command value of the object in the moving plan is set to be smaller than a feasible maximum moving velocity of the robot, restrictions by the restrictive condition hardly apply, as a matter of practice.
On the other hand, when moving the object at an angle with respect to the longitudinal direction of the robot or rotationally moving the object or moving the object sideways with respect to the robot, the following inconveniences are encountered if desired gaits are generated for the robot as described above.
For example, when the bipedal mobile robot is to move the object to the right of the robot by pushing the object, the right leg of the legs of the robot can usually make a relatively large step out in a direction in which the object is to be moved, whereas the left leg cannot actually make a large step out in the direction in which the object is to be moved because an influence of a restrictive condition for preventing interference or the like with the right leg. Hence, even if a desired gait for the robot is generated such that the position/posture of the robot will have an appropriate position-posture relationship with respect to desired position/posture of the object in the period of one step during which the right leg becomes a free leg, there are many cases where it is impossible to generate desired gaits for the robot such that the position/posture of the robot will establish an appropriate position/posture relationship with respect to desired position/posture of the object in the period of the next one step. As a result, it becomes difficult to move the object in exact accordance with a moving plan. This inconvenience applies also when rotationally moving the object or moving the object at an angle relative to the longitudinal direction of the robot.
Thus, according to the method for generating desired gaits such that the position/posture relationship between the robot and the object in the period of one step for each step of the robot, the leg on a free leg side is susceptible to a restrictive condition for preventing interference or the like of the leg on the free leg side with the leg on the supporting leg side, depending on a moving direction of the object relative to the robot. This inconveniently leads to, for example, frequent occurrence of a situation requiring a correction of a moving plan or the need for setting moving plans for each moving direction relative to the robot so as to adapt the moving plans to feasible motion modes of the legs of the robot.
The present invention has been made with a view of the above background and it is an object thereof to provide a gait creation device of a leg-type mobile robot which is capable of generating desired gaits of a robot that minimize situations in which a moving plan is required to be corrected and allow an object to be moved according to a moving plan as much as possible, regardless of the moving direction of the object relative to the robot.